1. Field of the Invention
The invention relates to a water pump that is driven by a driving force generated by an internal combustion engine, and a control method for the same.
2. Description of the Related Art
A water pump, which circulates a coolant in a water jacket, is used for an internal combustion engine. For example, Japanese Utility Model Application Publication No. 5-58832 (JP-U-5-58832) describes a water pump in which blades fitted to a rotational shaft (rotational body) are rotated to circulate a coolant. In the water pump, a driving force generated by the internal combustion engine is transmitted from a pulley, which is rotated in synchronization with the rotation of a crankshaft of the internal combustion engine, to the rotational shaft through a fluid coupling. Thus, the blades are rotated. In the water pump, as the temperature of the coolant in the water jacket becomes higher, a degree of engagement between the rotational shaft and the fluid coupling becomes higher. Thus, as the temperature of the coolant in the water jacket becomes higher, the driving force generated by the internal combustion engine is transmitted to the rotational shaft with a higher degree of efficiency.
In the water pump, it is preferable to control a circulation amount of the coolant based on an engine speed, the temperature of the coolant, and the load of the internal combustion engine. In this regard, in the water pump, the driving force generated by the internal combustion engine is transmitted from the pulley, which is rotated in synchronization with the rotation of the crankshaft of the internal combustion engine, to the rotational shaft. Therefore, as the engine speed becomes higher, the rotational speed of the rotational shaft becomes higher, and the circulation amount of the coolant becomes larger, as described above. In the control based on the temperature of the coolant and the load of the internal combustion engine, it is preferable to increase the circulation amount of the coolant by transmitting the driving force generated by the internal combustion engine to the rotational shaft with a high degree of efficiency, when the temperature of the coolant is high, and when the load of the internal combustion engine is high, as shown by a map in FIG. 6. However, in the water pump described in the above-described Japanese Utility Model Application Publication No. 5-58832 (JP-U-5-58832), the degree of transmission efficiency, with which the driving force is transmitted to the rotational shaft, is changed based on only the temperature of the coolant. Therefore, even when the load of the internal combustion engine is high, the rotational speed of the rotational shaft is not greatly increased, and the circulation amount of the coolant cannot be appropriately controlled, if the temperature of the coolant is low. Accordingly, for example, water pumps shown in FIG. 7 and FIG. 8 are examined. In each of the water pumps shown in FIG. 7 and FIG. 8, the rotational speed can be controlled in a manner shown by the map in FIG. 6. Hereinafter, the configurations of the water pumps will be described more specifically.
As shown in FIG. 7, a water pump 130 includes a circulation system 20 and a drive system 30 that functions as a drive portion. The circulation system 20 circulates a coolant. The drive system 30 drives a rotational cylinder 21 of the circulation system 20. A partition wall 40 is provided between the circulation system 20 and the drive system 30 to prevent the coolant from flowing into the drive system 30 from the circulation system 20.
A flow passage 23, through which the coolant flows, is formed in a cylinder block 22 of the internal combustion engine. A support shaft 25 whose one end is fixed to the partition wall 40 is provided in the flow passage 23. Bearings 24a and 24b are provided at respective ends of the support shaft 25. The support shaft 25 is fitted into the rotational cylinder 21 to which the blades 26 are attached. Thus, the rotational cylinder 21 is supported by the support shaft 25 in a manner such that the rotational cylinder 21 is rotatable relative to the support shaft 25. An induction ring 27, which includes an iron core, is fitted to an outer periphery of the rotational cylinder 21 at an end portion close to the partition wall 40.
A housing 31 is provided in the drive system 30. A pulley 32 is fixed to the housing 31. The pulley 32 is operatively connected to a crankshaft (not shown) of the internal combustion engine through a belt 33. A slider 34 is provided in the housing 31. A portion of the slider 34 is connected to the housing 31 through a spline. The slider 34 is reciprocated in the housing 31 along the axial direction of the rotational cylinder 21. A magnet 35 is attached to an end of the slider 34, which is close to the circulation system 20, in a manner such that the magnet 35 surrounds the induction ring 27 fitted to the outer periphery of the rotational cylinder 21. The magnet 35 is made of, for example, neodymium.
A spring 36 provided in the housing 31 constantly presses the slider 34 toward the circulation system 20. Torque transmitted from the crankshaft to the housing 31 through the belt 33 and the pulley 32 is transmitted to the rotational cylinder 21 by a magnetic force generated between the induction ring 27 and the magnet 35. Thus, the rotational cylinder 21 is rotated. When the blades 26 attached to the rotational cylinder 21 is rotated due to the rotation of the rotational cylinder 21, the coolant in the flow passage 23 is pressurized and delivered to a water jacket (not shown) of the internal combustion engine.
The inside of the housing 31 is divided into an atmosphere chamber 31a and a pressure chamber 31b by the slider 34. A seal member 37 is provided on the outer periphery of the slider 34 to provide sealing between the slider 34 and an inner peripheral surface of the housing 31. The pressure chamber 31b is kept air-tight by the seal member 37. When a pressure in the pressure chamber 31b changes, the slider 34 is reciprocated in the housing 1, and thus, the torque transmitted from the magnet 35 to the rotational cylinder 21 through the induction ring 27 is changed. Thus, in the water pump 130, the rotational cylinder 21 constitutes a rotational body driven by the reciprocating movement of the slider 34.
In the drive system 30, a pressure pipe 41 is inserted in the pressure chamber 31b of the housing 31. The pressure pipe 41 is supported by a bearing 42 provided in the housing 31, and fixed to another member (not shown). The housing 31 is rotatable relative to the pressure pipe 41. A seal portion 43 is provided between the pressure pipe 41 and the inner peripheral surface of the housing 31 to prevent leakage of air from the pressure chamber 31b. The pressure pipe 41 is connected to an electrically-controlled vacuum switching valve (hereinafter, referred to as “VSV”) 55 through a first passage 52. Further, the VSV 55 is connected to a portion of an intake passage 57, which is located downstream of a throttle valve 60, through a second passage 53. Also, the VSV 55 is connected to an atmospheric pressure space in an engine room through a third passage 54. An electronic control unit 50 controls the driving of the VSV 55 to switch the position of a valve element of the VSV 55. Thus, the pressure chamber 31b is selectively connected to one of the intake passage 57 and the atmospheric pressure space.
The electronic control unit 50 controls the driving of the VSV 55 in the manner described below. A vehicle is provided with, for example, an accelerator pedal sensor (not shown) that detects the amount of depression of an accelerator pedal, and other sensors that detect the load of the internal combustion engine. The cylinder block 22 is provided with a coolant temperature sensor 61 that measures the temperature of the coolant. When values detected by the sensors are input to the electronic control unit 50, the electronic control unit 50 changes the position of the valve element of the VSV 55 based on the map shown in FIG. 6.
That is, when the electronic control unit 50 determines that the temperature of the coolant is high, or determines that the temperature of the coolant is low and the load of the internal combustion engine is high, based on the values detected by, and received from the sensors, the electronic control unit 50 turns a control signal for the VSV 55 “ON” so that the pressure chamber 31b is connected to the atmospheric air space, and atmospheric air is introduced into the pressure chamber 31b. As a result, as shown in FIG. 7, there is no pressure difference between the atmosphere chamber 31a and the pressure chamber 31b, and therefore, the slider 34 is pressed by the pressing force of the spring 36, and displaced toward the circulation system 20. At this time, the magnet 35 provided in the slider 34 and the induction ring 27 provided in the rotational cylinder 21 face each other, and are close to each other. Thus, an amount of magnetic flux passing through the magnet 35 and the induction ring 27 is increased, and the rotational force transmitted from the slider 34 to the rotational cylinder 21 is relatively increased. This increases the amount of the coolant discharged and supplied into the water jacket due to the rotation of the blades 26.
When the electronic control unit 50 determines that the temperature of the coolant is low and the load of the internal combustion engine is low based on the values detected by, and received from the sensors, the electronic control unit 50 turns the control signal for the VSV 55 “OFF” so that the pressure chamber 31b is connected to the intake passage 57. In this situation, a pressure in the portion of the intake passage 57, which is located downstream of the throttle valve 60, is lower than the atmospheric pressure. Therefore, as shown in FIG. 8, the slider 34 is displaced toward the pressure pipe 41 against the pressing force of the spring 36, due to the pressure difference between the pressure chamber 31b and the atmosphere chamber 31a. Thus, the magnet 35 provided in the slider 34 is displaced away from the induction ring 27 provided in the rotational cylinder 21 in the axial direction of the rotational cylinder 21. As a result, the amount of magnetic flux passing through the magnet 35 and the induction ring 27 is decreased as compared to when the water pump 130 is in the state shown in FIG. 7. Accordingly, the flow rate of the coolant discharged and supplied into the water jacket is relatively decreased.
Thus, in the water pump 130, the position of the valve element of the VSV 55 is changed based on the map shown in FIG. 6 so that the coolant is appropriately circulated.
In the water pump 130, the electronic control unit 50 changes the position of the valve element of the VSV 55 by determining a point indicating the current operating state in the map shown in FIG. 6, based on the values detected by, and received from the sensors. Therefore, when the rotational speed of the rotational cylinder 21 is controlled in the water pump 130, the configuration of the control is complicated, and the load of the electronic control unit is high.